Uterine leiomyomas (fibroids) represent the most common tumor in women, disproportionately affect African- Americans, cause pregnancy loss, and induce excessive uterine bleeding leading to severe chronic anemia. Our long-term objective is to understand novel clinically relevant mechanisms responsible for the pathogenesis and growth of uterine leiomyomas in order to reduce associated morbidity. Our team has designed integrated projects focusing on paracrine interactions among leiomyoma cell populations and biologically critical signaling pathways involving RANKL/RANK, NR4A subfamily of nuclear receptors and AKT. Project I (Bulun) seeks to understand the mechanisms responsible for clonal expansion of a small but distinct stem cell population deficient in estrogen or progesterone receptors. Progesterone action, essential for the in vivo growth of leiomyomas, are transduced from steroid receptor-rich and mature leiomyoma cells onto the stem/progenitor cells via a paracrine signaling pathway involving the cytokine RANKL secreted by support cells for activating its receptor RANK in stem cells, triggering self-renewal and proliferation. Targetin RANK pathway in a unique stem cell population, responsible for regeneration and proliferation of leiomyomas, is a novel and clinically significant approach. Project II (Chakravarti/Nowak) was launched after system-wide expression profiling of the entire nuclear receptor family, which showed severe deficiencies of the NR4A subfamily expression in uterine leiomyomas. Project II will test the hypothesis that the NR4A members play critical and integrative roles involving TGF?3 and SMAD signaling in leiomyoma growth by regulating key proliferation and profibrotic genes. Elucidation of a novel role of a nuclear receptor subfamily deficiency in the context of proliferation and fibrosis is novel and a paradigm shift for identifying therapeutic targets. Projet III (Kim/Wei) will define the mechanisms that promote cellular senescence and death upon inhibition of AKT, which mediates the major signaling pathway for leiomyoma cell survival. Project III will test the hypothesis that the high oxidative stress levels in leiomyomas is able to promote growth and survival through the AKT pathway, however, upon inhibition of AKT, reactive oxygen species will induce miR-182, p16 and HMGA2 and cause senescence. AKT inhibition will also decrease BCL2 and enhances cell death. Pursuing AKT-dependent senescence and death pathways through ROS in uterine leiomyoma cells is both novel and translational. Optimally organized Administrative (Bulun) and Tissue/Cell (Wei/Marsh) Cores run by experienced Directors support these projects. Overall, all projects are clinically and thematically connected, collectively investigate self-renewal, proliferation, senescence and cell death in stem and differentiated cell populations of uterine fibroids, and are designed to introduce paradigm-shifting pathologic and therapeutic concepts. Just as the past funding period of this P01 Center led to the use of antiprogestins to treat uterine leiomyomas, we expect the development of novel treatments targeting RANKL/RANK, NR4A or AKT as a result of the proposed studies.